1. Field of the Invention
The invention relates to a cylinder-head gasket defining a sealing plane, and including at least a soft sheet of material made of a highly elastic layer of graphite, and formed with an opening serving as a fuel chamber passage, and wherein a sheet metal collar clamp extends along a rim of the layer bordering the opening.
2. Description of the Prior Art
Conventional cylinder-head gaskets consist of a sheet metal, which on both sides thereof is generally provided with a rubber-bonded asbestos-fiber soft-material layer so as to constitute a sealing plate. Such a sealing plate is formed with a plurality of openings in the form of one or several fuel chamber passages, as well as with openings for passage of oil and of a coolant. In the case of the fuel passages, a U-shaped sheet metal collar clamp extends at least along the rim bordering the opening.
The development of engines of constantly increasing output and of light-weight construction has led to some engine parts being subjected to increased stresses. Moreover, these engine parts are deformable, namely, they are deformed elastically during assembly and operation of the engine.
This development has led to the need of cylinder-head gaskets, which require easily deformable and highly elastic soft material layers, so that the cylinder head bolts need not be tightened too strongly. The integrity of the cylinder head gasket is therefore ensured, in spite of any deformations of engine parts required to be sealed with respect to one another.
If the conventional and generally horizontally disposed U-shaped sheet metal collar clamps are transferred from conventional metal-asbestos cylinder-head gaskets to cylinder-head gaskets with highly elastic soft material layers, then, due to bending along transition regions between the two flanges overlapping the sealing plate and the portion of the sheet metal collar clamp which borders the fuel chamber, there arise permanent fractures in such transition regions. Such fractures occur to an even higher degree, when cylinder head gaskets are used with highly elastic soft material layers, than in the case of metal-asbestos cylinder-head gaskets. The higher the elasticity of the soft material layers, the higher is the oscillation load to which these sheet metal collar clamps are subjected.
As there is a risk of permanent fracture occurring even in conventional metal-asbestos cylinder-head gaskets, the sheet metal collar clamps for the fuel chamber passages have already been made in two parts. A kind of collet is formed on one flange of the sheet metal collar clamp, which borders the fuel chamber passage, and is made to overlap with a similar collet of the other flange ( see German patent DE-OS No. 2236622). The considerably increased cost of manufacture of the cylinder-head gasket, is, however, a disadvantage of this embodiment.